The Alkynyl Moiety as a Donor for Donor-Acceptor Cyclopropanes

The first trans-selective [3 + 2]-cycloaddition of a new type of donor acceptor cyclopropane with aldehydes is presented. 2,2-Disubstituted cyclopropanes, bearing an allryne moiety as the sole donor entity, were transformed to highly substituted tetrahydrofurans in the presence of a catalytic amount of Ca(NTf2)(2)/Bu4NPF6. The protocol allows for an easy access to tetrahydrofurans bearing a versatile alkyne substituent at the quarternary 2-position under very mild reaction conditions.